It is desirable to miniaturise mass spectrometers and components thereof to produce smaller instruments, but also for other reasons such as in order to reduce the phase space volume of a component. For example, such phase space reduction may be particularly advantageous in preparing an ion beam for acceleration in Time of Flight (TOF) instruments. In particular, it is envisaged that aberrations of the ion beam in terms of the initial positions and velocity spreads of the ions may be reduced in order to increase the resolution of these instruments.
It is understood that in order reduce the geometric scale of a device that confines ions using an RF voltage, it is necessary to increase the frequency of the RF voltage correspondingly, in order to maintain stability of the confined ions. However, the effective potential generated by the RF voltage scales in inverse proportion to the square of the RF voltage frequency, so in order to create a strong enough effective potential for ion confinement the field strength must be increased according. Other difficulties also arise in miniaturising RF confinement devices. For example, difficulties may be encountered in miniaturising RF ions guides formed from stacks of ring electrodes or multipoles, since they comprise a relatively complex array of optical elements requiring individual voltage connections to adjacent optical elements.
U.S. Pat. No. 8,373,120 (Verentchikov) proposes a method of trapping ions by applying an RF voltage between a plate electrode and a wire mesh electrode, such that an oscillating electric field penetrates through the wire mesh in a direction away from the plate electrode. This penetrating field creates an array of effective potential barriers or wells corresponding to the pitch of the mesh. This device is relatively simple, since there are only a few macroscopic electrical connections required for the device.
It is desired to provide an improved ion manipulation device, an improved mass or ion mobility spectrometer, and an improved method of spectrometry.